1. Field of the Invention
This invention resides in asphalt technology and asphalt formulations, and also in waste management, particularly in connection with petroleum refinery operations.
2. Description of the Prior Art
As one of the world's greatest natural resources, petroleum is the source of a vast array of substances and materials used by consumers and industry alike. The petroleum refining industry has long served as the lifeblood of regions and economies worldwide and contributed to the standards of living currently enjoyed by consumers around the world. In addition to its many benefits to industry, commerce, and society, of course, petroleum refining generates large amounts of waste at various stages of its operations and in a variety of forms. These include wastewater sludges, tank bottoms, solids from slop oil emulsions, and sludges from separation units. The original means of disposing of these wastes, particularly those involving solids, was by landfill, either at the refinery itself or in commercial landfills, or by incineration, or both. Concerns about the environment and about the presence of toxic materials in soil and water have drawn public attention to many industrial and manufacturing operations, however, ultimately leading to the enaction in 1984 of the Hazardous and Solid Waste Amendments to the Resource Conservation and Recovery Act (RCRA).
In 1990, the Environmental Protection Agency implemented these Amendments by officially listing refinery wastes as hazardous wastes, assigning hazardous waste numbers to specified wastes such as dissolved air flotation (DAF) float (which includes up to 10% solids), slop oil emulsion solids, heat exchanger cleaning bundle sludge, API separator sludge, and leaded tank bottoms. The EPA imposed restrictions on the land disposal of these materials, prohibiting the disposal of these materials in landfills unless the materials were treated to reduce their hazardous constituents to extremely low concentrations or unless the landfill was specifically sanctioned by the EPA as one that ensured no migration of the hazardous constituents for as long as they remained hazardous. Other wastes that were soon added to the list were primary and secondary sludges from emulsified oil/water/solids separators and from tanks, impoundments, ditches, sumps and stormwater units, induced air flotation (IAF) units, and DAF units. The primary sludges are those collected by gravitational separation, while secondary sludges are those collected by physical or chemical separation. Solids from even more wastes are continually being added to the list.
These wastes are formed in large quantities in the typical refinery. At one refinery in northern California, waste solids are generated at a rate of 120 bags per day, each bag weighing 500 to 1,000 pounds, with a cost of disposal reaching $700.00 per ton. To lower this cost as well as satisfy the requirements imposed by the EPA, the industry has developed a variety of methods for waste processing and utilization. These include reclaiming useful oil from the wastes by thermal desorption, solvent extraction, and other physical and chemical processes, reintroducing the waste to the refinery as fuel, transporting the waste to an unrelated operation as fuel, and incineration either at the refinery or off-site. Many of these processes are costly, however, and many raise further concerns including the release of incineration products or volatilized substances into the atmosphere. In addition, the advanced refining technology continually being developed by the petroleum industry enables refiners to utilize lower grades of crude oil, generating even higher levels of waste.
The need for cost-effective waste disposal or utilization thus becomes increasingly critical to the petroleum industry as well as to the environment and to human health.
Of further relevance to the background of the present invention is a naturally occurring asphalt known as Trinidad Lake Asphalt, commonly referred to by its acronym TLA. This asphalt is mined from a pitch lake in the southwest of Trinidad. The lake, believed to have been discovered by Sir Walter Raleigh in 1595, is the largest commercial deposit of asphalt in the world. In its native form, TLA contains 30% water, which is readily removed by a simple refining process, leaving a molten material with a soluble bitumen content of 53–55% and a fine particulate mineral content of 36–37%. The lake is in a natural basin above a geological formation containing heavy crude oil. As the oil seeps upward, it passes through layers of rock, drawing the minerals from the rock and carrying them with it until it reaches the basin as a suspension of fine mineral particles in the crude oil. Once the oil is in the basin and exposed to the atmosphere, the light ends of the oil evaporate to leave the mineral-impregnated asphalt.
Trinidad Lake Asphalt is noted for its unusually high resistance to stress and environmental conditions, resulting in products that are highly durable with a long life and low maintenance. TLA and TLA-containing materials are particularly useful, for example, for the surfaces of roadways that receive high traffic, such as freeways, bridges, off-ramps, and the like, where they can be used at reduced thicknesses and yet perform at a level that is equivalent or better than that of other asphalts. In many applications, TLA is used as a binder for crushed mineral aggregate, typically ⅜–¾ inch (roughly 1–2 cm) in size, to form Stone Mastic Asphalt. Mastic asphalt in general (also referred to as asphalt mastic) is widely used as a building material in floors, paved areas, decks, and roofing.
A disadvantage of TLA is that it is a natural product from a single source, and while its value is recognized worldwide, the need to package and transport it to the sites of use adds to the cost.